Making the money and securing the money are two different sides. A different institution is responsible for making the money, while banks are responsible for securing it. Just because there are a lot of money in the bank doesn't mean that they are ones who are making money, there is a different institution responsible for it. Like here in our country, there is a different institution who's responsibility is making money rather than securing the money.
Then you really do not know much about how banks operate. Banks are not just there to be saving your money as they are not some charity saving organization. Your money is used for investment and majorly they make a lot from the money they lend, as they collect interest on loans, interest payment from debt securities, CDs as well as short term borrowings.
If they are not making any money at all, how do you think they will keep being operational? You think because they save money, money gets generated for them from thin air? No!